1. Field of the Invention
The present invention relates to a position detector capable of detecting the tilt and the rotation angle of, for example, a pen-shaped position pointer, and to a position pointer of the position detector.
2. Description of the Related Art
A pen-shaped position pointer is used, for example, to enter text and drawings. In this case, there is a demand to not only enter coordinate values as an input but also enter the rotation and tilt of the pen based, for example, on the manner in which the user twists his or her hand or on personal habits as data.
To respond to this demand, an invention has been proposed, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2014-35631) which is designed to detect the tilt angle of the position pointer on the sensor surface of the position detector or the rotation angle of the position pointer about the axis perpendicular to the sensor surface.
In Patent Document 1, first and second electrodes are provided on a core body to detect the rotation angle of the position pointer. The first and second electrodes are alternately selected to change the electrode from which to transmit an AC (alternating current) signal. At this time, signal transmission pattern information is included in the AC signal transmitted from the position pointer. The signal transmission pattern information indicates from which electrode, namely, the first or second electrode, an AC signal is transmitted.
The position detector calculates the rotation angle of the position pointer about the axis perpendicular to the sensor surface based on a plurality of coordinate positions on the sensor surface on which the AC signal from the position pointer has been received. The coordinate positions are found in relation to pattern information received from the position pointer.
Further, in Patent Document 1, three electrodes are provided on a housing to detect the tilt angle of the position pointer. Moreover, a switching circuit is provided which supplies an AC signal to one of the electrodes selected in advance based on a predetermined pattern. Then, the position pointer transmits, to the position detector, pattern information indicating the pattern type when the pattern is changed by the switching circuit.
The position detector calculates the tilt angle of the position pointer relative to the sensor surface from at least three coordinate positions and three signal intensities that are obtained for at least three pieces of pattern information received.
In this case, paragraph 0114 of Patent Document 1 states the following: “In the position pointer according to the present embodiment, three patterns or first, second and third patterns, are available. The first pattern selects only an electrode 40. The second pattern selects only an electrode 41. The third pattern selects only an electrode 42 . . . . When the first pattern is selected, a ‘code’ following a start signal is ‘0’ When the second or third pattern is selected, the ‘code’ following a start signal is ‘1.’ This allows the tablet to identify from which electrode of the position pointer the signal was transmitted in consideration of the transmission sequence described above.”
As described above, in the detection method of the position pointer's tilt angle in Patent Document 1, the position pointer does not transmit identification information about each of the three electrodes. Therefore, if it is difficult for the position detector to detect an AC signal from any of the three electrodes of the position pointer, it is difficult for the position detector to distinguish between the three patterns. As a result, it is likely that the position detector may not properly detect the rotation angle and the tilt angle.